1. Field of the Invention
This invention relates to thermally conductive silicone rubber compositions.
2. Description of the Prior Art
Heat-producing electronic components such as power transistors or thyristors generate heat in their operation with the result that their properties deteriorate over long periods due to the generation of heat and they occasionally fail. Conventionally, an insulating and radiating sheet is attached to a heat-producing electronic component to provide for the radiation of the heat generated or the electronic component is potted with a thermally conductive material. When a heat-fixer roll of a copy machine is made of the above-mentioned thermally conductive material, a sufficiently high temperature can be maintained at the roll surface even when the interior section (heated section) of the roll is at a low temperature. This is an advantage of a thermally conductive material.
Thermally conductive silicone rubber compositions may be used in a variety of applications as discussed above. Various types of thermally conductive silicone rubber compositions have been proposed to date. A typical example is an organoperoxide-vulcanized silicone rubber which is blended with aluminum oxide, beryllium oxide, hydrated aluminum oxide, or magnesium oxide as described in Japanese Kokai Pat. No. 55-22891.
However, such a thermally conductive silicone rubber composition is nonfluid and in solid form and therefore cannot be used as a potting material. Also, it is blended with high shearing force with a large amount of filler using a roll or Banbury mixer with the result that the blender is significantly abraded, resulting in a hindrance to the operation. This is a conventional drawback.
Another example is a radiating silicone rubber composition in which the principal components are a polydiorganosiloxane containing at least two vinyl groups per molecule, a polyorganohydrogensiloxane, a platinum compound, and fillers as described in Japanese Kokai Pat. No. 56-2349 published Jan. 12, 1981, to T. Endo. Alumina is cited as the filler in this patent. However, when attempting to mix a large amount of the usual alumina with a fluid silicone rubber composition, dispersion is poor or significant abrasion of the mixing equipment occurs with the result that the fluid silicone rubber composition becomes blackish. This results in poor external appearance on the part of the product. Moreover, it suffers from the drawback that the thermal conductivity can not be significantly improved even with the addition of a large quantity of alumina.